I found out for everybody (including INS) the distinguishing mark between terrorists and illegal immigrants:

Terrorists are mostly legally here as tourists. They have enough money and do not need to work in the US.

Illegal immigrants are working very hard for the salary near to minimum wage with no overtime money, sometimes getting no money for their work, and cannot complain. They have to care about family, job and how to pay bills all the time. They have to care for US citizen kids, but he has no right to work here.